Add request-level logging and metrics via Gadget middleware

[xortim]

Problem

There is no centralized request-level observability in Penny. Any logging or timing must be added inside individual handlers, leading to duplication or inconsistency. Gadget already tracks correlation IDs and request latency internally, but consumers have no way to hook into the pipeline.

What changes

Once Gadget supports middleware, register a logging/metrics middleware in cmd/server.go:

myBot.Use(func(next gadget.HandlerFunc) gadget.HandlerFunc {
    return func(ctx gadget.HandlerContext, ...) {
        start := time.Now()
        log.Info().Str("route", ctx.Route.Name).Msg("handling event")
        next(ctx, ...)
        log.Info().Dur("duration", time.Since(start)).Msg("done")
    }
})

This would provide consistent request logging across all handlers without modifying handler code.

Blocked by

• gadget-bot/gadget#80 — add middleware / hook system for request pipeline
• gadget-bot/gadget#78 — handler context (middleware signature depends on this)

Files affected

• cmd/server.go — register middleware after SetupWithConfig